The invention relates to a trenching plow, especially one for the formation of a constant cross-section, constant depth trench under water for the receipt of a pipe therein, and a method for utilizing the plow for laying pipe.
Trenching plows, per se, have existed for quite some time, such as those shown in U.S. Pat. Nos. 152,436 and 1,436,614. Forestry drainage plows are commercially-available for cutting V-shaped trenches in the earth, such as a Finnish plow called "Lokomo," and a plow made by W. Clark Ltd. at Park Gate in the United Kingdom. While such plows are generally useful, they are not readily adaptable for the formation of constant depth, constant cross-section trenches under water for laying pipe, or for other particular uses requiring constant depth, constant cross-section furrows under a wide variety of operating conditions and in a wide variety of soils. The plow according to the present invention is capable of forming a trench with constant cross-section and constant depth for the receipt of pipe therein, especially underwater trenches (although the plow of the invention may be utilized for formation of surface trenches).
The plow according to the invention includes a frame member with a tandem set of wheels mounted to a forward portion of the frame member. A share is mounted to the frame member posterior of the set of wheels, and mould boards are mounted with the share. A pair of coulters--knife, disc, or the like--are mounted to the frame interior of the share, one of the coulters being located on either side of a vertical plane generally containing the share. The coulters are mounted so that they cause soil failure inwards and decrease to minimum proportion the disturbance of the trench walls. Also, in underwater trenching, the coulters allow water into the sliding surface and thereby facilitate trenching. To ensure that the draft is not excessive, and to ensure that the coulters do not tend to lift the plow out of the ground, each of the coulters is arranged to rake forwardly at a positive angle .beta. to the horizontal, the angle .beta. being about 60.degree.-70.degree.. The blades are sharpened and set to give a clearance relative to the furrow wall, the coulters having a positive clearance angle .epsilon. of about 5.degree. to the trench side walls. The coulters extend to a depth less than the depth to which the share extends during trenching, preferably about two-thirds the depth. If a trench with sloping side walls is to be formed, the coulters are arranged to make a positive angle .DELTA. (corresponding to the angle that the side walls of the trench are to form) with respect to the horizontal, projections of the coulters forming a V.
According to another aspect of the present invention, a trenching plow is provided including a substantially linear frame member, a tandem set of wheels mounted anteriorly of, and to, said frame member, a share mounted to the posterior end of the frame member and mould boards mounted with the share, and the tandem set of wheels, share, and frame members arranged so that during trenching the frame member always makes a positive angle .alpha. with respect to the horizontal. (That is, the frame member is always inclined upwardly from the anterior to the posterior thereof.) The frame member includes a lower portion that is sharpened to a V which comprises means for splitting soil furrows formed by the share and mould boards during trenching. When knife coulters are provided in order to ensure that the furrow slicer is not squeezed, the coulters are staggered along the length of the frame member. The position of the wheels is adjustable, which adjustment assists in determining the depth of the trench to be formed, and means are provided for adjusting the shave angle of the share, said means including means for adjusting the position of the share with respect to the frame member including a shear pin operatively connecting the frame member to the share.
The trenching plow according to the invention is operable in any method of laying pipes substantially under water. The plow is towed at substantially constant speed, and a trench is formed having constant cross-section and constant depth, wherein natural particles transport of the spoils formed during cutting will re-heal the trench to some extent. The sides of the furrow in front of the plow are cut with coulters to allow water into the sliding surface, which water seepage facilitates the formation of the trench with the share, the penetration of the water reducing the drag forces on the plow. Pipe is then disposed in the constant cross-section, constant depth trench so formed. The plow may be pulled together with, as an integral part of, the pipe; or, the plow may be pulled separately before the pipe, or, the plow may be pulled ahead of the pipe in steps where the plow would be pulled over a given distance and then the pipe would be pulled over the same distance up to the plow, with the process being repeated over the entire length of the pipeline. The trench is preferably formed with side walls making an angle of about 60.degree. with respect to the horizontal--this minimizes the depth of trench one must form to properly lay pipe. According to the invention, it is possible to form a trench of about 1.1 meters depth in strong clay soil while maintaining a pulling speed of about two knots. As the pulling speed is reduced, the force necessary to form the trench is also reduced, however, it is of course desirable to have as high a speed as possible in order to reduce the time for formation of the trench in laying pipe.
It is the primary object of the present invention to provide a plow for formation of a trench having constant cross-section and constant depth, particularly for the laying of pipe therein. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.